The Organic Light Emitting Display (OLED) possesses many outstanding properties of self-illumination, low driving voltage, high luminescence efficiency, short response time, high clarity and contrast, near 180° view angle, wide range of working temperature, applicability of flexible display and large scale full color display. The OLED is considered as the most potential display device.
The OLED can be categorized into two major types according to the driving methods, which are the Passive Matrix OLED (PMOLED) and the Active Matrix OLED (AMOLED), i.e. two types of the direct addressing and the Thin Film Transistor (TFT) matrix addressing. The AMOLED comprises pixels arranged in array and belongs to active display type, which has high lighting efficiency and is generally utilized for the large scale display devices of high resolution.
The OLED display device is a spontaneous emission display device and is generally made of an ITO pixel electrode and a metal electrode respectively functioning as an anode and a cathode and an organic light emission layer arranged between the anode and the cathode. When a proper voltage is applied to the anode and the cathode, the organic light emission layer emits light. The organic light emission layer comprises a hole injection layer formed on the anode, a hole transport layer formed on the hole injection layer, an emissive layer formed on the hole transport layer, an electron transport layer formed on the emissive layer, and an electron injection layer formed on the electron transport layer. Light emitting mechanism is that when driven by a predetermined voltage, electrons and holes are respectively injected into the electron injection layer and the hole injection layer. The electrons and the holes migrate through the electron transport layer and the hole transport layer to the emissive layer and combine with each other in the emissive layer to form excitons that excite light-emitting molecules, the later undergoing radiation relaxation to give off visible light.
The OLED panel with large size will generate different IR drops at different positions due to the cathode electrode has a larger resistance, so the mura effect of the OLED panel will happen. Therefore, an auxiliary electrode connected to a cathode electrode is needed. The voltage applied on the cathode electrode via the auxiliary electrode could solve the mura effect due to the IR drop of the cathode electrode, so the display image of the OLED panel could be even and stable.